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TEM-1-encoding small plasmids impose dissimilar fitness costs on Haemophilus influenzae and Haemophilus

Annette Søndergaard1, Marianne Lund1, Niels Nørskov-Lauritsen1

  • 1Department of Clinical Microbiology, Aarhus University Hospital, Aarhus N, Denmark.

Microbiology (Reading, England)
|September 20, 2015
PubMed

Insights

Small plasmids carrying beta-lactamase genes are transferable between Haemophilus influenzae and Haemophilus parainfluenzae. TEM-1 plasmids show low fitness costs, while ROB-1 plasmids are unstable in H. parainfluenzae.

Area of Science:

  • Microbiology
  • Genetics
  • Molecular Biology

Background:

  • Haemophilus influenzae and Haemophilus parainfluenzae harbor distinct beta-lactamase profiles.
  • Small plasmids encoding beta-lactamases are key for antimicrobial resistance dissemination.

Purpose of the Study:

  • To investigate the fitness cost and stability of beta-lactamase-encoding plasmids in H. influenzae and H. parainfluenzae.
  • To understand the mechanisms of plasmid dissemination and their impact on bacterial fitness.

Main Methods:

  • Assessed plasmid stability and fitness cost using competition assays.
  • Quantified plasmid copy number and beta-lactamase gene expression via quantitative PCR.
  • Tested TEM-1, TEM-15, and ROB-1 plasmids in both bacterial species.

Main Results:

  • ROB-1 plasmid (pB1000) showed high curing rates in H. parainfluenzae, correlating with its absence in this species.
  • TEM-1 and TEM-15 plasmids (pSF3, pB1000) exhibited significant competitive disadvantages in both species.
  • Some fitness costs were linked to plasmid copy number and beta-lactamase mRNA expression levels.

Conclusions:

  • TEM-encoding plasmids are stably transferable between H. influenzae and H. parainfluenzae.
  • ROB-1 plasmid instability in H. parainfluenzae suggests host-specific adaptation.
  • TEM-1 plasmids confer varying fitness costs depending on the specific plasmid and host bacterium.

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